Surface water rushes along the surface of the Greeland ice sheet July 4, 2012. / Ian Joughin, AP

by Wendy Koch, USA TODAY

by Wendy Koch, USA TODAY

Sea levels will probably rise more now that the last remaining stable portion of Greenland's ice sheet - the world's second-largest - is no longer stable, a study says.

Scientists have known Greenland's ice sheet has been thinning for decades, but for the first time, they've found that's even occurring in its northeast region that had been stable for 25 years. Since 2003, the northeast's ice loss has nearly tripled.

The decline of Greenland's ice sheet, which is second in size only to Antarctica's and covers 80% of Greenland's surface, has been a major contributor to global sea level rise over the past 20 years. The study, published Sunday in the journal Nature Climate Change, says it's accounted for nearly one-sixth of annual sea level rise.

Largely because of rising air temperatures, an outlet glacier in the northeast has retreated at a pace of 12.4 miles over the past decade. That's much faster than the Jakobshavnglacier's retreat in southwest Greenland - 21.7 miles over the past 150 years.

How do scientists track this? They look at ice thickness measurements from four satellites as well as data from the Greenland GPS Network or GNET, which has 50 coastal stations that weigh the ice sheet like a giant bathroom scale.

They found that the northeast Greenland ice sheet started losing stability in 2003. Several particularly warm summers triggered increasing melting and calving events including several last year when chunks of ice fell from glaciers into the water.

This northeast region lost about 10 billion tons of ice per year from April 2003 to April 2012, the study says. The result is more water flowing into the oceans.

What particularly worries scientists is the impact on the rest of Greenland, because the northeast's ice stream stretches more than 370 miles into the continent's center and connects to the heart of its ice reservoir.

"It has the potential of significantly changing the total mass balance of the ice sheet in the near future," says study co-author Shfaqat Abbas Khan, senior researcher at the National Space Institute at the Technical University of Denmark. He and Bevis were joined by nine scientists from three other U.S. universities, the United Kingdom, Hong Kong and the Netherlands.